Heat exchangers for vehicles are known to have a header and a tank connected by tubes interspaced by fins, with sideplates providing rigidity. In this type of heat exchanger the fins provide a large surface area for heat transfer and support for the tubes.
Such heat exchangers may be used as radiators or condensers. They may also be used in a number of other applications including charged air coolers.
The sideplates are of particular importance during construction and handling of a heat exchanger. The sideplates may be used to gather the fins and tubes to form a heat exchanger core before securing the core to a header manifold and a tank manifold. Since it is preferable to provide the outermost tubes with fins on their outer edges to ensure good heat transfer, the sideplates may be attached to each of the outer fins.
After assembling the core assembly with the header manifold and the tank manifold, the resultant assembly is brazed in an oven. In the oven, braze cladding coated onto the components melts so that upon cooling, the components are secured together. Sideplates, as is known in the art, can be in a variety of shapes. For example, a sideplate may be a flat elongate plate or a plate curved at either side of an attachment surface. Sideplates may also have strengthening ribs. Suitable materials for sideplates include aluminum or aluminum alloys.
For production reasons, the assemblies are often put in the oven with the tubes positioned in the horizontal. A first problem which may arise with such positioning is "fin drop" which occurs between the fins and the sideplate during the oven melt period. In this condition, the fin begins to move from a symmetrically centered position relative to the sideplate center to an offset position. As a result, the core face edge of the fin is lower than the normal core face on one side and above the normal core face on the opposite side. Fin drop occurs when the force of gravity is greater than the residual friction force at the fin tip area that contacts the tubes and sideplate.
Radiator fins have been made which curl over the end radius of the tube. However, these fins do not always effectively prevent fin drop. Other fins use a bake framing member running close to the fin surface to prevent fin drop, but this can cause discoloration on the core surface or cratering if a clad build up is present.
A second problem is that of "fin dissolution". The brazing process has to be carried out in a reducing atmosphere to avoid production of metal oxides that would weaken the brazed joints. Unfortunately, during an effective reducing-atmosphere brazing process, the nature of the cladding is such that it causes diffusion of the adjacent material (i.e., the outer fins), which weakens the fin material and therefore the structural stability of the heat exchanger.
A third problem is that the materials of a bake frame, often comprising straps or wires, cause discoloration when in close proximity to cladded surfaces. Furthermore, if the frame material is in contact with the sideplates, the clad material tends to gather near the point of contact. This condition is known as "cratering" and results in marks on the surface of the sideplates. These phenomena reduce the aesthetic qualities of the heat exchanger.
It is accordingly an object of the present invention to at least partially mitigate the problems of the prior art.